consolidate logic for epoch and slot_index into Bank (#3144)

core/src/leader_schedule_utils.rs

@@ -32,8 +32,7 @@ fn sort_stakes(stakes: &mut Vec<(Pubkey, u64)>) {
 
 /// Return the leader for the given slot.
 pub fn slot_leader_at(slot: u64, bank: &Bank) -> Pubkey {
-    let slot_index = slot % bank.slots_per_epoch();
-    let epoch = slot / bank.slots_per_epoch();
+    let (epoch, slot_index) = bank.get_epoch_and_slot_index(slot);
 
     let leader_schedule = leader_schedule(epoch, bank);
     leader_schedule[slot_index as usize]

core/src/staking_utils.rs

@@ -176,7 +176,12 @@ mod tests {
     fn test_epoch_stakes_and_lockouts() {
         let validator = Keypair::new();
 
-        let (genesis_block, mint_keypair) = GenesisBlock::new(500);
+        let (mut genesis_block, mint_keypair) = GenesisBlock::new(500);
+
+        // makes the bank generate epoch_vote_accounts right on epoch boundaries
+        //   handy for tests
+        genesis_block.stakers_slot_offset = 0;
+
         let bank = Bank::new(&genesis_block);
         let bank_voter = Keypair::new();
 
@@ -190,13 +195,11 @@ mod tests {
         // should show up in the active set
         voting_keypair_tests::new_vote_account_with_vote(&mint_keypair, &bank_voter, &bank, 499, 0);
 
-        // Have to wait until the epoch at (stakers_slot_offset / slots_per_epoch) + 1
-        // for the new votes to take effect. Earlier epochs were generated by genesis
-        let epoch = (bank.stakers_slot_offset() / bank.slots_per_epoch()) + 1;
+        // Build a bank in the next epoch, it will generate an epoch_vote_accounts() for epoch 1
+        let epoch = 1;
         let epoch_slot = epoch * bank.slots_per_epoch();
-        let epoch_slot_offset = epoch_slot - bank.stakers_slot_offset();
 
-        let bank = new_from_parent(&Arc::new(bank), epoch_slot_offset);
+        let bank = new_from_parent(&Arc::new(bank), epoch_slot);
 
         let result: Vec<_> = epoch_stakes_and_lockouts(&bank, 0);
         assert_eq!(result, vec![(1, None)]);